SC runs only on 1 cylinder???

RazorRacer · 10-01-2008, 09:44 AM

After cranking with full throttle, the 79SC engine will run only on one cylinder as long as the pedal is too the metal???

Is this a symptom of a bad fuel pump check valve? What would allow the car to run on one cylinder at full throttle, but not fire the other five?

Notes:
1. This is an intermittent problem and only then do I crank with full throttle.
2. Car will run fine once fired up. About 1/2 of the time it fires right up.
3. The car will not run AT ALL with the fuel pump relay removed.
4. Vacuum system is fine because the pop off valve cannot be opened when cranking or running.
5. When running at idle, there is a loud sucking noise that can be heard when the air filter is removed.
6. Sometimes when running the car will stall and cannot be restarted.
7. Every wire from the CIS box to the engine has been checked by the highly effective means of vigorous shaking.
8. I smell gas when cranking.

This is my sons car and I am driving it so he won't stall out. Responses today will be helpful as I am leaving town and he will be without a ride for the weekend. I plan on changing the fuel pump this evening.

RazorRacer · 10-01-2008, 01:22 PM

Please don't respond to this unless you know the correct answer.

How many things will let the engine start on one cylinder with full throttle applied?

The engine is going ka-lug, ka-lug, ka-lug at about 100 rpm.

But the car runs great when it does fire up.

Pazuzu · 10-01-2008, 01:36 PM

Wait, it normally runs fine on all 6, but every now and then, when you try to start it, only one will fire? Then, if you apply full throttle and crank, it will eventually recover and run on all 6 again?

RazorRacer · 10-01-2008, 02:23 PM

When ever it runs, it always starts right up and runs fine, but might die during the trip. Sometimes it won't start and that is when it will run on one cylinder as long as I have the pedal to the metal. It will go like that forever, but never recover. I just come back every 10 minutes or so until it fires up.

jwernquist · 10-01-2008, 06:28 PM

Just from your comments above, it sounds like you should be taking the car in and having it professionally checked. Because people here will give you ideas whether they are correct or not they are things you need to check before replacing parts.

Theres no point in replacing the fuel pump because usually fuel pumps are not THAT intermittent.

Of course the car won't start with the fuel pump relay removed.

You need to be checking your cold and hot fuel pressures, if you feel that its a pressure issue however being as intermittent as it is. You will probably find out that its an ignition related issue.

However disregard my post because it's not the end all fix to your problem.

JW

carrera turbo · 10-01-2008, 06:44 PM

sounds like ignition, do a simple check while its chugging disconnect the plug wires from the car one at a time and
see if its getting spark.

you can also check to see if its a fuel delivery problem by taking a little carb clean and spraying under the fuel plate or through a vacume line to see if the motor changes from you 100 r.p.m. chug to a higher rev. if not goto the ignition system

ed

T77911S · 10-02-2008, 03:46 AM

Quote:

Originally Posted by RazorRacer

Please don't respond to this unless you know the correct answer.

How many things will let the engine start on one cylinder with full throttle applied?

The engine is going ka-lug, ka-lug, ka-lug at about 100 rpm.

But the car runs great when it does fire up.

thats not a very inviting statement if you want help.
there are exactly 64....umm..... 65 things that will let the engine start on one cylinder.

boyt911sc · boyt911sc's Garage

Do you have a CIS or carb? I may have missed it but please clarify. How on earth could you tell the engine was running on one (1) cylinder unless you have detached the other spark plug cables? Got a few ideas what could have caused your starting problem but not sure it will solve your problem. So I don't have the answers. Others might try......

TD

RazorRacer · 10-08-2008, 01:54 PM

Sorry to have been so curt, but I needed an answer quick to get my son running for the weekend. He ended up just getting rides from others. No big deal.

So, to continue the saga...

The car started running without "the intermittent problem", so much so, that he drove it to school the following week (yesterday). But then another problem developed where it would fire up and die immediately. Not knowing and following the suggestion of a friend, I took the CIS box out of my race car and put it into his car (side of the road in the rain), but the same problem. Again, this was a different problem (not really) because the car wouldn't even run on one cylinder. So before putting it on the trailer, I checked the mass-flow sensor and guess what? The pop off valve had completely popped out! We stuck it back into place and the car fired right up. So he has my CIS box and I have his CIS box and the car is running fine.

Final thoughts: I suspect there was a hairline crack in the epoxy around the pop off valve that would intermittently cause the car to act up. So anyone who said vacuum leak was correct.

I should have just stayed home last weekend because I crashed my MG Midget race car on the second lap of the first race and was done for the weekend.

RazorRacer · 10-11-2008, 11:05 AM

check that....the CDI box is bad. I'm at the track with his CDI box in my race car and it is doing the same thing...running on one cylinder but not firing up. I tapped the CDI box and it fired right up.

911pcars · 10-11-2008, 03:04 PM

FWIW, I don't think it's possible for 1 out of 6 cylinders to rotate the engine unless 5 are cut off after the crank has gained some serious rotation momentum. Even then, that's 1 power stroke per 2 revs of the crank from one cylinder.

How did you confirm 5 cylinders are dead or was that just a euphemistic term for "car runs like crap"?

Sherwood

RazorRacer · 10-12-2008, 08:17 PM

Well I didn't check spark on any of the cylinders if that's what you mean, but the engine was rotated by the crank and my foot was to the floor and it would run like that forever unless I took my foot off the gas. It's definitely CIS box related because the switched CIS boxes (see above) switched the problem from one car to the other. It was running around 100 rpm on what appeared to be one cylinder. Is that better?